Posted on by Jason Major

A Virtual Galactic Smash-Up!

An online simulator for galactic collisions (Adrian Price-Whelan/Columbia University)

Have you ever had the desire to build your own galaxies, setting your own physical parameters and including as many stars as you want, and then smash them together like two toy cars on a track? Well, now you can do just that from the comfort of your own web browser (and no waiting billions of years for the results!)

This interactive online app by Adrian Price-Whelan lets you design a galaxy, including such parameters as star count, radius and dispersion rate, and then create a second galaxy to fling at it. Clicking and dragging on the black area will send the invading galaxy on its course, letting you watch the various results over and over again. (If those SMBH’s hit, look out!)

In reality many galaxies have gone through (or are going through, from our perspective) such collision events, our own Milky Way being no exception. In fact, the Milky Way is on course to collide with the Andromeda Galaxy… in about 4 billion years.

So while we wait patiently for that, this is just a bit of addictive fun to distract you from your Cyber Monday shopping spree. Enjoy!

(Source: Columbia University Astronomy & Physics)

Inset image: Hubble interacting galaxies UGC 9618, 450 million light-years away. Credit: NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University)

Posted on by Nancy Atkinson

The Milky Way’s Black Hole Shoots Out Brightest Flare Ever

This false-color image shows the central region of our Milky Way Galaxy as seen by Chandra. The bright, point-like source at the center of the image was produced by a huge X-ray flare that occurred in the vicinity of the supermassive black hole at the center of our galaxy.
Image: NASA/MIT/F. Baganoff et al.

For some unknown reason, the black hole at the center of the Milky Way galaxy shoots out an X-ray flare about once a day. These flares last a few hours with the brightness ranging from a few times to nearly one hundred times that of the black hole’s regular output. But back in February 2012, astronomers using the Chandra X-Ray Observatory detected the brightest flare ever observed from the central black hole, also known as Sagittarius A*. The flare, recorded 26,000 light years away, was 150 times brighter than the black hole’s normal luminosity.

What causes these outbursts? Scientists aren’t sure. But Sagittarius A* doesn’t seem to be slowing down, even though as black holes age they should show a decrease in activity.

Mysterious X-ray flares caught by Chandra may be asteroids falling into the Milky Way's giant black hole. Credit: X-ray: NASA/CXC/MIT/F. Baganoff et al.; Illustrations: NASA/CXC/M.Weiss

Earlier this year, a group of researchers said that the outbursts may come from asteroids or even wandering planets that come too close to the black hole and they get consumed. Basically, the black hole is eating asteroids and then belching out X-ray gas.

Astronomers involved in this new observation seem to concur with that line of thinking.

“Suddenly, for whatever reason, Sagittarius A* is eating a lot more,” said Michael Nowak, a research scientist at MIT Kavli and co-author of a new paper in the Astrophysical Journal. “One theory is that every so often, an asteroid gets close to the black hole, the black hole stretches and rips it to pieces, and eats the material and turns it into radiation, so you see these big flares.”

Astronomers detect black holes by the light energy given off as they swallow nearby matter. The centers of newborn galaxies and quasars can appear extremely bright, giving off massive amounts of energy as they devour their surroundings. As black holes age, they tend to slow down, consuming less and appearing fainter in the sky.

“Everyone has this picture of black holes as vacuum sweepers, that they suck up absolutely everything,” says Frederick K. Baganoff, another co-author from MIT. “But in this really low-accretion-rate state, they’re really finicky eaters, and for some reason they actually blow away most of the energy.”

While such events like this big blast appear to be relatively rare, Nowak suspects that flare-ups may occur more frequently than scientists expect. The team has reserved more than a month of time on the Chandra Observatory to study Sagittarius A* in hopes of identifying more flares, and possibly what’s causing them.

“These bright flares give information on the flaring process that isn’t available with the weaker ones, such as how they fluctuate in time during the flare, how the spectrum changes, and how fast they rise and fall,” said Mark Morris from UCLA. “The greatest importance of this bright flare may be that it builds up the statistics on the characteristics of strong flares that can eventually be used to [identify] the cause of such flares.”

Even more intriguing to Baganoff is why the black hole emits so little energy. In 2003, he ran the very first observations with the then-new Chandra Observatory, and calculated that, given the amount of gas in its surroundings, Sagittarius A* should be about a million times brighter than it is — a finding that suggested the black hole throws away most of the matter it would otherwise consume.

The physics underlying such a phenomenon remain a puzzle that Baganoff and others hope to tease out with future observations.

“We’re really studying the great escape, because most of the gas escapes, and that’s not what we expect,” Baganoff says. “So we’re piecing out the history of the activity of the center of our galaxy.”

Paper: Chandra/HETGS Observations of the Brightest Flare seen from Sgr A*

See a movie of the flare here.

Source: MIT

Posted on by Nancy Atkinson

Astronomers Find Ultimate Oxymoron: A Small Supermassive Black Hole

There’s jumbo shrimp and accurate rumors; now there’s even a mini supermassive black hole. Astronomers have identified the smallest supermassive black hole ever observed, and while it’s considered a shrimp as far as supermassive black holes go, this guy is still pretty big: the mass of the black hole in galaxy NGC 4178 is estimated to be about 200,000 times the mass of our Sun. But it was a surprise that this galaxy had a black hole at all.

Astronomers using the Chandra X-Ray Observatory in conjunction with other observatories took a look at NGC 4178, a late-type spiral galaxy located about 55 million light years from Earth. It does not contain a bright central concentration, or bulge, of stars in its center, and so it was thought that perhaps this galaxy was one of the few that didn’t harbor a black hole.

With using Chandra’s X-Ray vision, as well as infrared data the NASA’s Spitzer Space Telescope and radio data from the Very Large Array, Nathan Secrest, from George Mason University and his team identified a weak X-ray source at the center of the galaxy, and also saw varying brightness at infrared wavelengths, suggesting that a black hole was actually in the center of NGC 4178 and was pulling in material from its surroundings. The same data also suggested that light generated by this infalling material is heavily absorbed by gas and dust and was therefore surrounding a black hole.

They were able to estimate the size of the black hole by using the known relationship between the mass of a black hole and the amount of X-rays and radio waves it generates.

While this is the lowest mass supermassive black holes ever observed, astronomers admit this is probably near the extreme low-mass end of being in the “supermassive” range. And as the team pointed out in their paper, there is increasing evidence that several late-type galaxies do host supermassive black holes, and that a classical bulge is not a requirement for a supermassive black hole to form and grow.

Read the team’s paper.

Source: NASA

Posted on by Jenny Winder

Integral: Ten Years Tracking Extreme Radiation Across the Universe

Caption: Artist’s impression of ESA’s orbiting gamma-ray observatory Integral. Image credit: ESA

Integral, ESA’s International Gamma-Ray Astrophysics Laboratory launched ten years ago this week. This is a good time to look back at some of the highlights of the mission’s first decade and forward to its future, to study at the details of the most sensitive, accurate, and advanced gamma-ray observatory ever launched. But the mission has also had some recent exciting research of a supernova remnant.

Integral is a truly international mission with the participation of all member states of ESA and United States, Russia, the Czech Republic, and Poland. It launched from Baikonur, Kazakhstan on October 17th 2002. It was the first space observatory to simultaneously observe objects in gamma rays, X-rays, and visible light. Gamma rays from space can only be detected above Earth’s atmosphere so Integral circles the Earth in a highly elliptical orbit once every three days, spending most of its time at an altitude over 60 000 kilometres – well outside the Earth’s radiation belts, to avoid interference from background radiation effects. It can detect radiation from events far away and from the processes that shape the Universe. Its principal targets are gamma-ray bursts, supernova explosions, and regions in the Universe thought to contain black holes.

5 metres high and more than 4 tonnes in weight Integral has two main parts. The service module is the lower part of the satellite which contains all spacecraft subsystems, required to support the mission: the satellite systems, including solar power generation, power conditioning and control, data handling, telecommunications and thermal, attitude and orbit control. The payload module is mounted on the service module and carries the scientific instruments. It weighs 2 tonnes, making it the heaviest ever placed in orbit by ESA, due to detectors’ large area needed to capture sparse and penetrating gamma rays and to shield the detectors from background radiation in order to make them sensitive. There are two main instruments detecting gamma rays. An imager producing some of the sharpest gamma-ray images and a spectrometer that gauges gamma-ray energies very precisely. Two other instruments, an X-ray monitor and an optical camera, help to identify the gamma-ray sources.

During its extended ten year mission Integral has has charted in extensive detail the central region of our Milky Way, the Galactic Bulge, rich in variable high-energy X-ray and gamma-ray sources. The spacecraft has mapped, for the first time, the entire sky at the specific energy produced by the annihilation of electrons with their positron anti-particles. According to the gamma-ray emission seen by Integral, some 15 million trillion trillion trillion pairs of electrons and positrons are being annihilated every second near the Galactic Centre, that is over six thousand times the luminosity of our Sun.

A black-hole binary, Cygnus X-1, is currently in the process of ripping a companion star to pieces and gorging on its gas. Studying this extremely hot matter just a millisecond before it plunges into the jaws of the black hole, Integral has discovered that some of it might be escaping along structured magnetic field lines. By studying the alignment of the waves of high-energy radiation originating from the Crab Nebula, Integral found that the radiation is strongly aligned with the rotation axis of the pulsar. This implies that a significant fraction of the particles generating the intense radiation must originate from an extremely organised structure very close to the pulsar, perhaps even directly from the powerful jets beaming out from the spinning stellar core.

Just today ESA reported that Integral has made the first direct detection of radioactive titanium associated with supernova remnant 1987A. Supernova 1987A, located in the Large Magellanic Cloud, was close enough to be seen by the naked eye in February 1987, when its light first reached Earth. Supernovae can shine as brightly as entire galaxies for a brief time due to the enormous amount of energy released in the explosion, but after the initial flash has faded, the total luminosity comes from the natural decay of radioactive elements produced in the explosion. The radioactive decay might have been powering the glowing remnant around Supernova 1987A for the last 20 years.

During the peak of the explosion elements from oxygen to calcium were detected, which represent the outer layers of the ejecta. Soon after, signatures of the material from the inner layers could be seen in the radioactive decay of nickel-56 to cobalt-56, and its subsequent decay to iron-56. Now, after more than 1000 hours of observation by Integral, high-energy X-rays from radioactive titanium-44 in supernova remnant 1987A have been detected for the first time. It is estimated that the total mass of titanium-44 produced just after the core collapse of SN1987A’s progenitor star amounted to 0.03% of the mass of our own Sun. This is close to the upper limit of theoretical predictions and nearly twice the amount seen in supernova remnant Cas A, the only other remnant where titanium-44 has been detected. It is thought both Cas A and SN1987A may be exceptional cases

Christoph Winkler, ESA’s Integral Project Scientist says “Future science with Integral might include the characterisation of high-energy radiation from a supernova explosion within our Milky Way, an event that is long overdue.”

Find out more about Integral here
and about Integral’s study of Supernova 1987A here

Posted on by John Williams

Monster Black Holes Lurk at the Edge of Time

The reddish object in this infrared image is ULASJ1234+0907, located about 11 billion light-years from Earth. The red color comes from vast amounts of dust, which absorbs bluer light, and obscures the supermassive black hole from view in visible wavelengths. Credit: image created using data from UKIDSS and the Wide-field Infrared Survey Explorer (WISE) observatory.

As if staring toward the edge of the Universe weren’t fascinating enough, scientists at the University of Cambridge say they see enormous, rapidly growing supermassive black holes barely detectable near the edge of time.

Thick dust shrouds the monster black holes but they emit vast amounts of radiation through violent interactions and collisions with their host galaxies making them visible in the infrared part of the electromagnetic spectrum. The team published their results in the journal Monthly Notices of the Royal Astronomical Society.

The most remote object in the study lies at a whopping 11 billion light-years from Earth. Ancient light from the supermassive black hole, named ULASJ1234+0907 and located toward the constellation of Virgo, the Maiden, has traveled (at almost 10 trillion kilometers, or 6 million million miles, per year) across the cosmos for nearly the estimated age of the Universe. The monster black hole is more than 10 billion times the mass of our Sun and 10,000 times more massive than the black hole embedded in the Milky Way Galaxy; making it one of the most massive black holes ever seen. And it’s not alone. Researchers say that there may be as many as 400 giants black holes in the tiny sliver of the Universe that we can observe.

“These results could have a significant impact on studies of supermassive black holes” said Dr Manda Banerji, lead author of the paper, in a press release. “Most black holes of this kind are seen through the matter they drag in. As the neighbouring material spirals in towards the black holes, it heats up. Astronomers are able to see this radiation and observe these systems.”

The team from Cambridge used infrared surveys being carried out on the UK Infrared Telescope (UKIRT) to peer through the dust and locate the giant black holes for the first time.

“These results are particularly exciting because they show that our new infrared surveys are finding super massive black holes that are invisible in optical surveys,” says Richard McMahon, co-author of the study. “These new quasars are important because we may be catching them as they are being fed through collisions with other galaxies. Observations with the new Atacama Large Millimeter Array (ALMA) telescope in Chile will allow us to directly test this picture by detecting the microwave frequency radiation emitted by the vast amounts of gas in the colliding galaxies.”

Huge black holes are known to reside at the centers of all galaxies. Astronomers predict the most massive of these cosmic phenomena grow through violent collisions with other galaxies. Galactic interactions trigger star formation which provides more fuel for black holes to devour. And it’s during this process that thick layers of dust hide the munching black holes.

“Although these black holes have been studied for some time,” says Banergi, “the new results indicate that some of the most massive ones may have so far been hidden from our view. The newly discovered black holes, devouring the equivalent of several hundred Suns every year, will shed light on the physical processes governing the growth of all supermassive black holes.”

Astronomers compare the extreme case of ULASJ1234+0907 with the relatively nearby and well-studied Markarian 231. Markarian 231, found just 600 million light-years away, appears to have recently undergone a violent collision with another galaxy producing an example of a dusty, growing black hole in the local Universe. By contrast, the more extreme example of ULASJ1234+0907, shows scientists that conditions in the early Universe were more turbulent and inhospitable than today.

Source: Royal Astronomical Society

Image Credit: Markarian 231, an example of a galaxy with a dusty rapidly growing supermassive black hole located 600 million light years from Earth. The bright source at the center of the galaxy marks the black hole while rings of gas and dust can be seen around it as well as “tidal tails” left over from a recent impact with another galaxy. Courtesy of NASA/ESA Hubble Space Telescope.

Posted on by Nancy Atkinson

Rare X-Ray Nova Reveals a New Black Hole in the Milky Way

Swift J1745-26, with a scale of the moon as it would appear in the field of view from Earth. This image is from September 18, 2012 when the source peaked in hard X-rays. Credit: NASA/Goddard Space Flight Center/S. Immler and H. Krimm

Back in mid-September, the Swift satellite was going about its multi-wavelength business of watching for bursts of bright gamma-ray, X-ray, ultraviolet, or optical events in the sky, when it detected a rising tide of high-energy X-rays from a source toward the center of our Milky Way galaxy. But this was different from any other burst the satellite had detected, and after observing the event for a few days, astronomers knew this had to be a rare X-ray nova. What it meant was that Swift had detected the presence of a previously unknown stellar-mass black hole.

“Bright X-ray novae are so rare that they’re essentially once-a-mission events and this is the first one Swift has seen,” said Neil Gehrels from Goddard Space Flight Center, the mission’s principal investigator. “This is really something we’ve been waiting for.”

The object was named Swift J1745-26 after the coordinates of its sky position, the nova is located a few degrees from the center of our galaxy toward the constellation Sagittarius. While astronomers do not know its precise distance, they think the object resides about 20,000 to 30,000 light-years away in the galaxy’s inner region.

An X-ray nova is a short-lived X-ray source that appears suddenly in the sky and dramatically increases in strength over a period of a few days and then decreases, fading out over a few months. Unlike a conventional nova, where the compact component is a white dwarf, an X-ray nova is caused by material – usually gas — falling onto a neutron star or a black hole.

The rapidly brightening source triggered Swift’s Burst Alert Telescope twice on the morning of Sept. 16, and once again the next day.

Ground-based observatories detected infrared and radio emissions, but thick clouds of obscuring dust have prevented astronomers from catching Swift J1745-26 in visible light.

The nova peaked in hard X-rays — energies above 10,000 electron volts, or several thousand times that of visible light — on Sept. 18, when it reached an intensity equivalent to that of the famous Crab Nebula, a supernova remnant that serves as a calibration target for high-energy observatories and is considered one of the brightest sources beyond the solar system at these energies.

Even as it dimmed at higher energies, the nova brightened in the lower-energy, or softer, emissions detected by Swift’s X-ray Telescope, a behavior typical of X-ray novae. By Wednesday, Swift J1745-26 was 30 times brighter in soft X-rays than when it was discovered and it continued to brighten.

“The pattern we’re seeing is observed in X-ray novae where the central object is a black hole. Once the X-rays fade away, we hope to measure its mass and confirm its black hole status,” said Boris Sbarufatti, an astrophysicist at Brera Observatory in Milan, Italy, who currently is working with other Swift team members at Penn State in University Park, Pa.

Here’s usually happens in events like this: The black hole is part of a binary system with a normal Sun-like star. A stream of material flows into an accretion disk around the black hole. Usually, the disk of gas spirals in steadily to the black hole, heats up and produces a steady X-ray glow. But sometimes, for reasons unknown, the material is held up in the outer regions, held back by some mechanism, almost like a dam. Once enough gas accumulates, the dam breaks and a flood of gas surges towards the black hole, creating the X-ray nova outburst.

“Each outburst clears out the inner disk, and with little or no matter falling toward the black hole, the system ceases to be a bright source of X-rays,” said John Cannizzo, a Goddard astrophysicist. “Decades later, after enough gas has accumulated in the outer disk, it switches again to its hot state and sends a deluge of gas toward the black hole, resulting in a new X-ray outburst.”

This phenomenon, called the thermal-viscous limit cycle, helps astronomers explain transient outbursts across a wide range of systems, from protoplanetary disks around young stars, to dwarf novae — where the central object is a white dwarf star — and even bright emission from supermassive black holes in the hearts of distant galaxies.

It is estimated that our galaxy must harbor some 100 million stellar-mass black holes. Most of these are invisible to us, and only about a dozen have been identified.

Swift discovers about 100 bursts per year. The Burst Alert Telescope detects GRBs and other events and accurately determines their positions on the sky. Swift then relays a 3 arcminute position estimate to the ground within 20 seconds of the initial detection, enabling ground-based observatories and other space observatories the chance to observe the event as well. The Swift spacecraft itself “swiftly” –in less than approximately 90 seconds — and autonomously repoints itself to bring the burst location within the field of view of the sensitive narrow-field X-ray and UV/optical telescopes to observe the afterglow and gather data.

Source: NASA

Posted on by Nancy Atkinson

Two Stars Do a Short-Orbit Tango Around the Milky Way’s Black Hole

Astronomers have known for some time there was one star orbiting fairly close to the black hole at the center of our galaxy. But now another star has been found dipping close and orbiting even faster around the Milky Way’s central black hole. Astronomer Andrea Ghez from UCLA says the ability to watch these two stars in a short-period ‘tango’ around the black hole will help scientist measure the effects of space-time curvature, and they should be able to determine whether Albert Einstein was right in his prediction of how black holes could warp space and time.

“I’m extremely pleased to find two stars that orbit our galaxy’s supermassive black hole in much less than a human lifetime,” said Ghez. “It is the tango of [these stars] that will reveal the true geometry of space and time near a black hole for the first time. This measurement cannot be done with one star alone.”

There are nearly 3,000 stars that orbit somewhat close to the black hole, and most of them have orbits of 60 years or longer.
The previously known close-in star, S0-2, orbits the black hole every 15.5 years. And now, the newly found star, called S0-102, orbits the black hole in a blazing 11.5 years, the shortest known orbit of any star near this black hole.

Reconstruction of the orbits of two stars—S0-2 and S0-102—near the black hole at the Milky Way’s center. (Other stars’ orbits are also depicted by fainter lines.) The background is a real high-resolution infrared image of the region. Credit: Andrea Ghez et al./UCLA/Keck

In the same way that planets orbit around the sun, S0-102 and S0-2 are each in an elliptical orbit around the central black hole. Ghez said that the planetary motion in our solar system was the ultimate test for Newton’s gravitational theory 300 years ago, and now the motion of S0-102 and S0-2 will be the ultimate test for Einstein’s theory of general relativity, which describes gravity as a consequence of the curvature of space and time.

“The exciting thing about seeing stars go through their complete orbit is not only that you can prove that a black hole exists but you have the first opportunity to test fundamental physics using the motions of these stars,” Ghez said. “Showing that it goes around in an ellipse provides the mass of the supermassive black hole, but if we can improve the precision of the measurements, we can see deviations from a perfect ellipse — which is the signature of general relativity.”

As the stars come to their closest approach, their motion will be affected by the curvature of spacetime, and the light traveling from the stars to us will be distorted, Ghez said.

S0-2, which is 15 times brighter than S0-102, will go through its closest approach to the black hole in 2018. S0-102 makes its closest approach in 2021, so the team will be keeping an eye on these stars as they get tantalizingly close, but not close enough to get sucked in, Ghez said.

Ghez and her colleagues have been observing S0-2 since 1995. In 2000, she and her team reported — for the first time – that astronomers had seen stars accelerate around the supermassive black hole. Their research demonstrated that three stars had accelerated by more than 250,000 mph a year as they orbited the black hole. The speed of S0-102 and S0-2 should also accelerate by more than 250,000 mph at their closest approach, Ghez said.

“The fact that we can find stars that are so close to the black hole is phenomenal,” said Ghez. “Now it’s a whole new ballgame, in terms of the kinds of experiments we can do to understand how black holes grow over time, the role supermassive black holes play in the center of galaxies, and whether Einstein’s theory of general relativity is valid near a black hole, where this theory has never been tested before. It’s exciting to now have a means to open up this window.”

The research was done using the Keck Telescopes. The team’s paper was published Oct. 5 in the journal Science.

Source: UCLA

Lead image caption: The Keck I and Keck II telescopes focus on two stars orbiting Milky Way’s black hole. Background photo credit: Dan Birchall/Subaru Telescope on Mauna Kea, Hawaii. Overlay created by Professor Andrea Ghez and her research team at UCLA and are from data sets obtained with the W. M. Keck Telescopes.

Posted on by Jason Major

What Happens When Supermassive Black Holes Merge?

Frame from a simulation of the merger of two black holes and the resulting emission of gravitational radiation (NASA/C. Henze)

The short answer? You get one super-SUPERmassive black hole. The longer answer?

Well, watch the video below for an idea.

This animation, created with supercomputers at the University of Colorado, Boulder, show for the first time what happens to the magnetized gas clouds that surround supermassive black holes when two of them collide.

The simulation shows the magnetic fields intensifying as they contort and twist turbulently, at one point forming a towering vortex that extends high above the center of the accretion disk.

This funnel-like structure may be partly responsible for the jets that are sometimes seen erupting from actively feeding supermassive black holes.

The simulation was created to study what sort of “flash” might be made by the merging of such incredibly massive objects, so that astronomers hunting for evidence of gravitational waves — a phenomenon first proposed by Einstein in 1916 — will be able to better identify their potential source.

Read: Effects of Einstein’s Elusive Gravity Waves Observed

Gravitational waves are often described as “ripples” in the fabric of space-time, infinitesimal perturbations created by supermassive, rapidly rotating objects like orbiting black holes. Detecting them directly has proven to be a challenge but researchers expect that the technology will be available within several years’ time, and knowing how to spot colliding black holes will be the first step in identifying any gravitational waves that result from the impact.

In fact, it’s the gravitational waves that rob energy from the black holes’ orbits, causing them to spiral into each other in the first place.

“The black holes orbit each other and lose orbital energy by emitting strong gravitational waves, and this causes their orbits to shrink. The black holes spiral toward each other and eventually merge,” said astrophysicist John Baker, a research team member from NASA’s Goddard Space Flight Center. “We need gravitational waves to confirm that a black hole merger has occurred, but if we can understand the electromagnetic signatures from mergers well enough, perhaps we can search for candidate events even before we have a space-based gravitational wave observatory.”

The video below shows the expanding gravitational wave structure that would be expected to result from such a merger:

If ground-based telescopes can pinpoint the radio and x-ray flash created by the mergers, future space telescopes — like ESA’s eLISA/NGO — can then be used to try and detect the waves.

Read more on the NASA Goddard new release here.

First animation credit: NASA’s Goddard Space Flight Center/P. Cowperthwaite, Univ. of Maryland. Second animation: NASA/C. Henze.

 

Posted on by Fraser Cain

Using Gravity to Peer into the Most Violent Places in the Universe: Colliding Black Holes

Simulation of colliding black holes

Simulation of colliding black holes

Nothing matches the destructive power of a black hole; a singularity of dense matter with a gravitational pull so strong that nothing, not even light can escape. What goes in, doesn’t come back out. And so you can imagine how difficult it would be to probe the region inside a black hole’s event horizon. And yet, there’s a catastrophic event that should give scientists a momentary glance into the maelstrom, to partly understand what’s going on “in there.” That event would be the collision between two black holes.

As you probably know, there’s a supermassive black hole lurking at the heart of every galaxy. As these galaxies merge, these black holes encounter one another too. Sometimes a black hole is violently kicked into deep space, and other times they merge together into an even more super-supermassive black hole. The collision happens out of sight, beneath the shared event horizon. So, there’s no way to see what’s going on … and live to tell about it.

By looking at the gravity, however, astronomers might be able to peer right into the collision zone. One of the predictions made by Albert Einstein, as part of his famous General Theory of Relativity, is that dramatic gravitational events in the Universe, like the formation or collision of black holes should be detectable by the gravitational waves they generate. As these waves wash over us, the ripples in spacetime should be detectable by extremely sensitive instruments or spacecraft flying in formation.

A team of researchers from Cardiff University, Ioannis Kamaretsos, Mark Hannam and B. Sathyaprakash, have used a powerful supercomputer to simulate what kinds of gravitational waves might be generated by merging black holes. Two black holes orbiting one another should be emitting gravitational waves and gradually losing energy. This causes them to spiral inward, collide, and create a black hole which is highly deformed.

According to their simulation, the gravitational waves from this deformed black hole will give off a distinctive “tone”, like a ringing bell. In fact, by measuring only this tone, astronomers will be able to deduce both the mass of the black hole and the speed of its spin. Furthermore, the distortion of the gravitational waves should allow researchers to “see” what’s going on within the black hole’s event horizon; to understand what happened to the merging monsters after they disappeared beneath the shared event horizon.

“By comparing the strengths of the different tones, it is possible not only to learn about the final black hole, but also the properties of the original two black holes that took part in the collision,” Ioannis Kamaretsos said in a news release.

Of course, it’s important to note that gravitational waves themselves are still purely theoretical. Even though there are multiple ground-based detectors already built, and even more sensitive space-based detectors on the way, there hasn’t been a direct detection of a gravitational wave yet, only indirect detections. However, I wouldn’t bet against Einstein. He’s had a pretty good track record.

Original Source: Cardiff News Release

Posted on by Nancy Atkinson

Hot Dog! WISE Finds a Bounty of Black Holes

From a NASA press release:

NASA’s Wide-field Infrared Survey Explorer (WISE) mission has led to a bonanza of newfound supermassive black holes and extreme galaxies called hot DOGs, or dust-obscured galaxies.

Images from the telescope have revealed millions of dusty black hole candidates across the universe and about 1,000 even dustier objects thought to be among the brightest galaxies ever found. These powerful galaxies, which burn brightly with infrared light, are nicknamed hot DOGs.

“WISE has exposed a menagerie of hidden objects,” said Hashima Hasan, WISE program scientist at NASA Headquarters in Washington. “We’ve found an asteroid dancing ahead of Earth in its orbit, the coldest star-like orbs known and now, supermassive black holes and galaxies hiding behind cloaks of dust.”

WISE scanned the whole sky twice in infrared light, completing its survey in early 2011. Like night-vision goggles probing the dark, the telescope captured millions of images of the sky. All the data from the mission have been released publicly, allowing astronomers to dig in and make new discoveries.

The latest findings are helping astronomers better understand how galaxies and the behemoth black holes at their centers grow and evolve together. For example, the giant black hole at the center of our Milky Way galaxy, called Sagittarius A*, has 4 million times the mass of our sun and has gone through periodic feeding frenzies where material falls towards the black hole, heats up and irradiates its surroundings. Bigger central black holes, up to a billion times the mass of our sun, may even shut down star formation in galaxies.

In one study, astronomers used WISE to identify about 2.5 million actively feeding supermassive black holes across the full sky, stretching back to distances more than 10 billion light-years away. About two-thirds of these objects never had been detected before because dust blocks their visible light. WISE easily sees these monsters because their powerful, accreting black holes warm the dust, causing it to glow in infrared light.

This zoomed-in view of a portion of the all-sky survey from WISE shows a collection of quasar candidates. Image credit: NASA/JPL-Caltech/UCLA

“We’ve got the black holes cornered,” said Daniel Stern of NASA’s Jet Propulsion Laboratory, Pasadena, Calif., lead author of the WISE black hole study and project scientist for another NASA black-hole mission, the Nuclear Spectroscopic Telescope Array (NuSTAR). “WISE is finding them across the full sky, while NuSTAR is giving us an entirely new look at their high-energy X-ray light and learning what makes them tick.”

In two other WISE papers, researchers report finding what are among the brightest galaxies known, one of the main goals of the mission. So far, they have identified about 1,000 candidates.

These extreme objects can pour out more than 100 trillion times as much light as our sun. They are so dusty, however, that they appear only in the longest wavelengths of infrared light captured by WISE. NASA’s Spitzer Space Telescope followed up on the discoveries in more detail and helped show that, in addition to hosting supermassive black holes feverishly snacking on gas and dust, these DOGs are busy churning out new stars.

“These dusty, cataclysmically forming galaxies are so rare WISE had to scan the entire sky to find them,” said Peter Eisenhardt, lead author of the paper on the first of these bright, dusty galaxies, and project scientist for WISE at JPL. “We are also seeing evidence that these record setters may have formed their black holes before the bulk of their stars. The ‘eggs’ may have come before the ‘chickens.'”

More than 100 of these objects, located about 10 billion light-years away, have been confirmed using the W.M. Keck Observatory on Mauna Kea, Hawaii, as well as the Gemini Observatory in Chile, Palomar’s 200-inch Hale telescope near San Diego, and the Multiple Mirror Telescope Observatory near Tucson, Ariz.

The WISE observations, combined with data at even longer infrared wavelengths from Caltech’s Submillimeter Observatory atop Mauna Kea, revealed that these extreme galaxies are more than twice as hot as other infrared-bright galaxies. One theory is their dust is being heated by an extremely powerful burst of activity from the supermassive black hole.

“We may be seeing a new, rare phase in the evolution of galaxies,” said Jingwen Wu of JPL, lead author of the study on the submillimeter observations. All three papers are being published in the Astrophysical Journal.

The three technical journal articles, including PDFs, can be found at http://arxiv.org/abs/1205.0811, http://arxiv.org/abs/1208.5517 and http://arxiv.org/abs/1208.5518 .

Lead image caption: With its all-sky infrared survey, NASA’s Wide-field Infrared Survey Explorer, or WISE, has identified millions of quasar candidates. Image credit: NASA/JPL-Caltech/UCLA